485
FXUS62 KGSP 220608
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
208 AM EDT Sat Jun 22 2024

.SYNOPSIS...
A hot and humid subtropical airmass returns to the area this
weekend, lingering through much of next week and leading to heat
indices in the upper 90s to lower 100s east of the mountains Sunday
through Thursday. Isolated diurnal showers and thunderstorms return
to the mountains today, with scattered activity possible area-wide
Sunday into Monday as a weak cold front tracks across the area.
Drier conditions are expected Tuesday into Wednesday before a
stronger cold front brings better coverage of shower and
thunderstorms late Wednesday into Thursday.

&&

.NEAR TERM /THROUGH TODAY/...
As of 130 AM Sat: Mostly clear over the CWA at this hour under
influence of upper anticyclone in the lower MS Valley and weak
sfc high pressure centered off the Atlantic coast. Compact sfc
low sitting near St Simons Island GA remains too distant to have
direct impact in our area, but maritime airmass is spreading inland
on its north flank, evidenced by 70-74 dewpoints in the northern
SC Midlands. This air will creep into the lower Catawba Valley and
Charlotte metro by around dawn, and could bring some low cloud cover
with it. The moisture advection will continue today as the sfc low
drifts inland into South GA, but with the incumbent air being rather
dry through a deep layer, diurnal mixing will slow the moistening
trend from mid-morning through early afternoon. Subsidence is
still evident aloft, although inversion is a little more likely
to be overcome owing to the slightly warmer sfc T/Td, with SE sfc
flow still being the only real forcing. The models that correctly
depicted minimal coverage yesterday over the mountains are doing
so again today. Still think a mention of isolated showers and more
isolated thunderstorms is reasonable in that area, with overall
PoP pretty similar to previous fcst. Still not confident enough
to mention PoP for most of the Piedmont, except in our southeast
border areas where the more humid air will become established
earlier in the day, and a slight-chance is included. Max temps
will inch a degree or two warmer compared to Friday, ending up at
91-93 for most of the Piedmont and around 90 in the major mountain
valleys. Dewpoints should mix out into the upper 60s and this
should be enough to keep heat index below 100.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
Key Messages:

1) Hot and Humid Conditions Continue into Monday, Especially East of
the Mountains

2) Heat Indices may Flirt with Heat Advisory Criteria in the Upper
Savannah River Valley Monday Afternoon

3) A Weak Cold Front Increases Shower and Thunderstorm Chances
Slightly Sunday into Monday

As of 130 AM EDT Saturday: No major changes to the short term
forecast period this update. A large upper anticyclone will remain
parked over the Southern Plains/Desert Southwest while an upper
trough digs south across the East Coast through the short term. At
the sfc, a weak cold front will track across the Midwest Sunday into
Sunday night before pushing across the western Carolinas Monday into
Monday night. This front should allow for at least scattered shower
and thunderstorm development Sunday into Monday. Capped PoPs to
chance (50% or less) for now as global models are still not in
agreement regarding the exact timing/coverage of convection. Drier
conditions are expected Monday night behind the front as sfc high
pressure builds into the region. Despite the cold front, hot and
humid conditions will linger through the period. Highs east of the
mountains should reach into the low to mid 90s with heat indices
climbing into the upper 90s/lower 100s each afternoon, especially
across the Upper Savannah River Valley and along I-77. Heat indices
should generally remain below Heat Advisory Criteria but may flirt
with criteria on Monday in the the Upper Savannah River Valley.
Highs will end up around 7-9 degrees above climo each day. Lows
Sunday night will be around 8-10 degrees above climo, becoming 4-7
degrees above climo Monday night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 215 PM EDT Friday: The aforementioned upper trough will
continue to push offshore as we move into the extended to be
replaced by a secondary shortwave by midweek as upper ridging over
the Desert Southwest dominates. This will allow a more substantial
cold front to drop out of Canada and through the OH Valley towards
the Southern Appalachians by the end of the period. However, before
we can get there, we have to get through still very warm days on
Tuesday and Wednesday, with highs currently progged in the upper 90s
across portions of the Piedmont, and low to mid 90s in some mountain
valleys. Post-frontal dewpoints Tuesday drop off just a tad with dry
downslope flow so heat indices with the current forecast are not
quite as oppressive, but moisture return on Wednesday may lead to
increased dewpoints and higher heat indices, so later forecasts will
refine this. Minimal diurnal convective activity in the mountains
Tuesday but increasing activity as the front approaches Wednesday,
with enhanced pops (likelies in the mountains) by the end of the
period. For now, the approaching front knocks us down to just above
normal temps for Thursday but global guidance in disagreement on how
quickly the front pushes through.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Light SE flow will advect moist maritime
air to near KCLT by dawn and has prompted TEMPO for MVFR cigs, with
IFR not out of the question. Mountain valleys likely will develop
fog but once again not extensive enough to reach KAVL. Elsewhere
VFR this period. Sfc winds initially will be light/VRB at the
terminals aside from KCLT, but should pick up from the SE after
daybreak and veer toward S by afternoon. Low VFR cu will develop by
midday; some could linger or even develop anew after sunset owing
to weak sfc convergence near leading edge of maritime airmass. A
stray SHRA or even TSRA will be possible this aftn and evening
in the mountains but with such weak forcing this was not likely
enough to include at KAVL.

Outlook: Expect a return to more typical scattered convection across
the region Sunday and Monday.  Slight drying may follow for Tuesday.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$

SYNOPSIS...AR
NEAR TERM...Wimberley
SHORT TERM...AR
LONG TERM...TDP
AVIATION...Wimberley